Process and equipment for hot moulding of articles made of thermoplastic material

ABSTRACT

A process for the hot moulding of articles (L) made of thermoplastic material, comprising the steps of:  
     heating at least one plate of thermoplastic material (L) to a plasticizing temperature;  
     compressing said heated plate (L) between two moulding surfaces ( 14, 16 ), set opposite one another, of a pair of half-moulds ( 10, 12 ); and  
     forming, by injection moulding, at least one component ( 22 ) anchored to a surface of the plate (L), while the plate is being compressed between said moulding surfaces ( 14, 16 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process and equipment for thehot moulding of articles made of thermoplastic material.

[0003] 2. State of the Art

[0004] The invention has been developed in particular for the mouldingof panels for lining the interiors of motor vehicles. A conventionaltechnology for the production of lining panels involves heating of atleast one plate of thermoplastic material to a plasticizing temperatureand setting the plate, together with a possible upholstery sheet,between two half-moulds of an apparatus for hot moulding, which areprovided with respective moulding surfaces set opposite one another. Hotmoulding involves the application of pressure on opposite surfaces ofthe plate in a plastic state, thus bestowing on the plate the desiredshape. Normally, during moulding of the plate, also an upholstery sheetis applied on one surface of the plate itself When panels are producedfor internal lining of motor vehicles, it is often necessary to fix, onthe rear surface of the panel, one or more inserts forming an anchoringseat for a fixing means, such as a screw, a snap-in pin, or the like.Normally, these inserts are produced by injection moulding separatelyfrom the hot moulding of the panel, and are subsequently fixed bywelding on the rear surface of the moulded plate. Alternatively, theinserts produced by injection moulding may be fixed on the plate duringhot moulding of the plate itself In this case, the inserts arepositioned in the hot-moulding equipment and are mechanically anchoredto the plate during moulding.

[0005] The latter approach requires injection-moulding equipmentindependent of the hot-moulding equipment and involves an operating stepin which the inserts are fixed onto the moulded plates, or else a stepin which the inserts are positioned on the moulding equipment.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to provide a process andequipment for hot moulding of articles made of thermoplastic material,which will enable a reduction in the cost of the finished articles and asimplification of the production cycle.

[0007] According to the present invention, the above subject is achievedby a process and equipment having the characteristics specified in theclaims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] The present invention will now be described in detail withreference to the attached drawings, which are provided purely to furnisha non-limiting example, and in which:

[0009]FIG. 1 is a schematic partial section of hot-moulding equipmentaccording to the present invention;

[0010]FIGS. 2 and 3 are schematic sections illustrating the equipment ofFIG. 1 in various steps of the operating cycle;

[0011]FIG. 4 is a schematic perspective view of the part indicated bythe arrow IV in FIG. 3; and

[0012]FIG. 5 is a detail at an enlarged scale of the part indicated bythe arrow V in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0013] With reference to FIGS. 1-3, the numbers 10 and 12 respectivelydesignate a top half-mould and a bottom half-mould of a hot-mouldingapparatus. The half-moulds 10, 12 have respective moulding surfaces 14,16, which are set opposite each other and are designed to apply amoulding pressure on a plate L of thermoplastic material, following uponmovement from an open position to a closed position.

[0014]FIG. 1 illustrates the half-moulds in a closed position, at theend of hot moulding of the plate L. The plate L is first heated up to aplasticizing temperature and is set between the two half-moulds 10, 12while these are in the open position. An upholstery sheet R may be setbetween the two half-moulds together with the plate L so that it will beapplied on one surface of the plate L during moulding of the latter. Thehalf-moulds 10, 12 are provided, in a conventional way, with a coolingsystem in order to ensure that, during the moulding operation, the plateL will be cooled down to a temperature substantially lower than theplasticizing temperature of the thermoplastic material.

[0015] One of the two half-moulds (in the example illustrated, thebottom half-mould 12) is provided with at least one injection-mouldingseat 18, which communicates with an injection channel 20. The seat 18 isdesigned to form an insert 22 having, for instance, the shapeillustrated in FIG. 4. The insert 22, illustrated to provide an examplein FIG. 4, comprises a portion 24 containing a hole 26 with its axissubstantially orthogonal to the plate L. The portion 24 is connected tothe plate L₃ via three walls 28 fixed to the plate L, each along one ofits edges 30.

[0016]FIG. 1 illustrates the configuration of the moulding equipment atthe end of the hot-moulding step and before injection of plasticmaterial into the injection-moulding seat 18. The seat 18 definedbetween one portion of the mould 12 and a slider 32 which is mobile withrespect to the half-mould 12 to enable extraction of the insert 22 thatis formed in the seat 18. The slider 32 has a surface 34 whichconstitutes a portion of the hot-moulding surface of the half mould 12.

[0017] As may be seen in FIG. 1, the moulding seat 18 communicates withthe hote moulding surface 16, 34 by means of a narrow section 36 whichconstitutes the joining edge 30 between the insert 22 and the plate L.The narrow section 36 has a surface substantially smaller than that ofthe transverse section of the remaining part of the cavity 18, so as toproduce, at the narrow section 36, a marked reduction in the pressure ofthe plastic material injected into the moulding seat 18.

[0018] With reference to FIG. 2, after hot moulding of the plate L hasbeen completed, and after partial cooling of the plate L by contact withthe half-moulds 10, 12, plastic material compatible with thethermoplastic matrix of the plate L is injected into the injection.moulding seat 18. The injection of plastic material is performedaccording to a technology typical of injection moulding of plasticmaterials. For example, the plastic material may be propylenee based andmay be injected at pressures in the region of 600-1000 bar and at atemperature in the region of 180° C. The narrow section 36 of contactbetween the moulding seat 18 and the plate L reduces the pressureagainst the plate L of the injected material and thus prevents theinjected material from damaging the plate L and the upholstery sheet R.The dimensions of the narrow section 36 can be varied according to theparameters of the injection process so as to prevent damage to the plateand, at the same time, to obtain a surface for mutual fixing between theinsert 22 and the plate L that is sufficiently large for providing firmanchorage.

[0019] As illustrated in FIG. 3, after the insert 22 has been obtainedby injection moulding, the half-moulds 10, 12 are brought into the openposition and, at the same time, the slider 32 is displaced with respectto the half-mould 12 in the direction indicated by the arrow A so as toenable extraction of the insert 22 from the seat 18. As illustrated inFIGS. 3 and 5, the insert 22 is anchored to the plate L along the edge30 having a narrow section. The number of inserts 22 fixed to the plateL may vary according to the particular requirements. Also the shape andsize of each insert 22 may vary widely with respect to what is describedand illustrated herein purely for the purpose of providing an example.

1. A process for the hot moulding of articles made of thermoplasticmaterial, comprising the steps of: heating at least one plate ofthermoplastic material to a plasticizing temperature; compressing saidheated plate between two moulding surfaces, set opposite one another, ofa pair of half-moulds; and forming, by injection moulding, at least onecomponent anchored to a surface of the plate, while the plate is beingcompressed between said moulding surfaces.
 2. A process according toclaim 1 , wherein the injection moulding of the aforesaid component isperformed by injecting plastic material at high pressure into a seatcommunicating with one of said moulding surfaces.
 3. A process accordingto claim 2 , wherein said seat presents a narrow section designed toproduce a reduction in the pressure of the plastic material injected incontact with the plate.
 4. A process according to claim 1 , comprisingthe step of displacing a slider defining one part of said seat forextracting the injection-moulded component from the respective seat. 5.Equipment for hot moulding of articles made of thermoplastic material,comprising a first half-mould and a second half-mould which are free tomove with respect to one another between an open position and a closedposition and are provided with respective moulding surfaces designed tocarry out hot moulding of at least one plate of thermoplastic material,at least one of said half-moulds comprising at least oneinjection-moulding seat communicating with the respective hot-mouldingsurface, at least one injection channel being provided for injectingplastic material inside said seat.
 6. Equipment according to claim 5 ,wherein the said injection-moulding seat presents a narrow sectiondesigned to reduce the pressure of the plastic material injected incontact with the plate.
 7. Equipment according to claim 5 , wherein thehalf-mould provided with said injection-moulding seat carries a sliderwhich is mobile with respect to the half-mould between an operatingposition in which the slider defines a part of said injection-mouldingseat and a non-operating position in which the injection-mouldedcomponent can be extracted from the seat.